Six speed motorcycle transmission

ABSTRACT

A six speed gear assembly for a motorcycle transmission is provided that includes a mainshaft gear shaft with a plurality of mainshaft gears mounted in sequence thereon, wherein the sequence includes a mainshaft 4th gear, a mainshaft 3rd gear, one of a mainshaft 1st gear and a mainshaft 2nd gear, the other of the mainshaft 1st gear and the mainshaft 2nd gear, a mainshaft 6th gear, and a mainshaft 5th gear. The six speed gear assembly also includes a countershaft gear shaft with a plurality of countershaft gears mounted in sequence thereon, wherein the sequence includes a countershaft 4th gear, a countershaft 3rd gear, one of a countershaft 1st countershaft 1st gear and a countershaft 2nd gear, the other of the countershaft 1st gear and the countershaft 2nd gear, a countershaft 6th gear, and a countershaft 5th gear.

FIELD OF THE INVENTION

The present invention relates generally to a six speed gear assemblyand/or components related thereto for use in a six speed transmissioncase. Alternatively or in addition, the present invention relatesgenerally to a six speed gear assembly and/or components related theretofor retrofitting to a five speed transmission case.

BACKGROUND OF THE INVENTION

It is often desirable to remove a stock Harley Davidson® five speedmotorcycle transmission from a Harley Davidson® motorcycle and replacethe it with a six speed transmission to convert the motorcycle from afive speed transmission to a six speed transmission. For ease ofinstallation, it is desirable to mount a six speed gear assembly into anexisting stock Harley Davidson® five speed transmission case to convertthe transmission from a five speed transmission to a six speedtransmission.

However, since the stock Harley Davidson® five speed transmission caseis designed to receive a stock Harley Davidson® five speed gearassembly, conventional six speed gear assemblies do not fit into thestock Harley Davidson® five speed transmission case. Accordingly, a needexists for a six speed gear assembly and/or components related theretothat may be mounted in a stock Harley Davidson® five speed transmissioncase. A need also exists for a six speed gear assembly and/or componentsrelated thereto that may be mounted in a stock Harley Davidson® fivespeed transmission without modifying the outer dimensions of the stockHarley Davidson® five speed transmission case and without modifying themotorcycle exhaust.

SUMMARY

In one embodiment, the present invention is a six speed gear assemblyfor a motorcycle transmission that includes a mainshaft gear shaft witha plurality of mainshaft gears mounted in sequence thereon, wherein thesequence includes a mainshaft 4th gear, a mainshaft 3rd gear, one of amainshaft 1st gear and a mainshaft 2nd gear, the other of the mainshaft1st gear and the mainshaft 2nd gear, a mainshaft 6th gear, and amainshaft 5th gear. The six speed gear assembly also includes acountershaft gear shaft with a plurality of countershaft gears mountedin sequence thereon, wherein the sequence includes a countershaft 4thgear, a countershaft 3rd gear, one of a countershaft 1st countershaft1st gear and a countershaft 2nd gear, the other of the countershaft 1stgear and the countershaft 2nd gear, a countershaft 6th gear, and acountershaft 5th gear.

In another embodiment, the present invention is a six speed gearassembly for a motorcycle transmission that includes a mainshaft gearshaft having a plurality of mainshaft gears mounted thereon, wherein theplurality of mainshaft gears includes 1st, 2nd, 3rd, 4th, 5th andmainshaft 6th gears. The six speed gear assembly also includes acountershaft gear shaft having a plurality of countershaft gears mountedthereon, wherein the plurality of countershaft gears includes 1st, 2nd,3rd, 4th, 5th and countershaft 6th gears. Each mainshaft gear mesheswith a corresponding countershaft gear to form a plurality of gearcouplings. One of the gears from each gear coupling is rotatably coupledto its corresponding gear shaft and the remaining gear from each gearcoupling is non-rotatably coupled to its corresponding gear shaft. Eachrotatably coupled gear includes pockets that removably engage dogs thatprotrude from one of a plurality of shift rings, and wherein each shiftring is non-rotatably coupled to a corresponding one of the gear shafts.

In yet another embodiment, the present invention is a method ofretrofitting a six speed motorcycle transmission to a stock HarleyDavidson® five speed transmission case, wherein the stock case includesa central portion, a first side wall adjacent to a first side of thecentral portion, and a stock trapdoor adjacent to a second side of thecentral portion, and wherein the central portion includes a top surfaceand a central portion opening. The method includes removing the stocktrapdoor; providing a six speed gear assembly having a mainshaft gearshaft and a countershaft gear shaft; mounting a plurality of mainshaftgears on the mainshaft, wherein the plurality of mainshaft gearsincludes mainshaft 1st, 2nd, 3rd, 4th, 5th and 6th gears; and mounting aplurality of countershaft gears on the countershaft, wherein theplurality of countershaft gears includes countershaft 1st, 2nd, 3rd,4th, 5th and 6th gears. Each mainshaft gear meshes with a correspondingcountershaft gear to form a plurality of gear couplings. The method alsoincludes securing the six speed gear assembly to a replacement trapdoor.The replacement trapdoor includes a recess that receives at least aportion of the thickness of one of the gear couplings. The method alsoincludes securing the replacement trapdoor and the six speed gearassembly to the stock case.

In still another embodiment, the present invention is a trapdoor forretrofitting to a stock Harley Davidson® five speed transmission case,that includes a trapdoor base; and a recess in the trapdoor base forreceiving at least a portion of the thickness of a gear from a six speedgear assembly.

In still yet another embodiment, the present invention is a trapdoor fora motorcycle transmission that includes a trapdoor base; and a recess inthe trapdoor base for receiving at least a portion of the thickness of agear from a transmission gear assembly.

In a further embodiment, the present invention is a trapdoor and endcover combination for a motorcycle transmission that includes a trapdoorbase having a protrusion extending therefrom; and an end cover basehaving a recess formed therein, wherein the protrusion of the trapdoormates with the recess in the end cover to prevent a rotational movementof the trapdoor relative to the end cover.

In a still further embodiment, the present invention is a transmissionassembly that includes a six speed gear assembly having a mainshaft gearshaft and a countershaft gear shaft. A plurality of mainshaft gears aremounted on the mainshaft. The plurality of mainshaft gears includesmainshaft 1st, 2nd, 3rd, 4th, 5th and 6th gears. A plurality ofcountershaft gears are mounted on the countershaft. The plurality ofcountershaft gears includes countershaft 1st, 2nd, 3rd, 4th, 5th and 6thgears. Each mainshaft gear meshes with a corresponding countershaft gearto form a plurality of gear couplings. The transmission assembly alsoincludes a trapdoor having a recess that receives at least a portion ofthe thickness of one of the gear couplings.

BRIEF DESCRIPTION OF THE DRAWINGS

Novel features and advantages of the present invention will be betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is an exploded perspective view of a stock Harley Davidson® fivespeed motorcycle transmission according to the prior art;

FIG. 2 is an exploded perspective view of an exemplary six speed gearassembly according to one aspect of the present invention as well as anexemplary trapdoor according to another aspect of the invention forreceiving the six speed gear assembly and an exemplary end coveraccording to another aspect of the invention for attachment to thetrapdoor;

FIGS. 3A and 3B are perspective and side views, respectively, of a shiftring for use with the six speed gear assembly according to an exemplaryembodiment of the present invention;

FIGS. 4A and 4B are perspective and side views, respectively, of anothershift ring for use with a six speed gear assembly according to anexemplary embodiment of the present invention;

FIGS. 5A and 5B are side and cross-sectional views, respectively, of afirst exemplary gear for use with a six speed gear assembly according toan exemplary embodiment of the present invention;

FIGS. 6A and 6B are side and cross-sectional views, respectively, of asecond exemplary gear for use with a six speed gear assembly accordingto an exemplary embodiment of the present invention;

FIGS. 7A and 7B are side and cross-sectional views, respectively, of thetrapdoor of FIG. 2, with FIG. 7B being taken from line 7B—7B of FIG. 7Aand rotated 180 degrees;

FIGS. 8A and 8B are side and cross-sectional views, respectively, of theend cover of FIG. 2;

FIG. 9 is an exploded perspective view of the six speed gear assembly,the trapdoor and the end cover of FIG. 2, as well as a stock HarleyDavidson® five speed transmission case, an exemplary shift assemblyaccording to another aspect of the present invention and an exemplaryshift pawl according to another aspect of the present invention;

FIG. 10 is an enlarged perspective view of the shift assembly shown inFIG. 9;

FIGS. 11A and 11B are side and front views, respectively, of anexemplary shift fork according to another aspect of the invention foruse with a shift assembly according to an exemplary embodiment of thepresent invention;

FIGS. 12A and 12B are side and front views, respectively, of a shiftfork for use with a shift assembly according to an exemplary embodimentof the present invention;

FIGS. 13A and 13B are side and front views, respectively, of a shiftfork for use with a shift assembly according to an exemplary embodimentof the present invention;

FIG. 14 is a side view of an exemplary six speed gear assembly accordingto one aspect of the present invention shown in a neutral gear position;

FIG. 15 is a side view of an exemplary six speed gear assembly accordingto one aspect of the present invention shown in a 1st gear position;

FIG. 16 is a side view of an exemplary six speed gear assembly accordingto one aspect of the present invention shown in a 2nd gear position;

FIG. 17 is a side view of an exemplary six speed gear assembly accordingto one aspect of the present invention shown in a 3rd gear position;

FIG. 18 is a side view of an exemplary six speed gear assembly accordingto one aspect of the present invention shown in a 4th gear position;

FIG. 19 is a side view of an exemplary six speed gear assembly accordingto one aspect of the present invention shown in a 5th gear position;

FIG. 20 is a side view of an exemplary six speed gear assembly accordingto one aspect of the present invention shown in a 6th gear position;

FIG. 21A is a cross-sectional view taken from line 21A—21A of FIG. 10showing a detent track mounted to a shift drum of the shift assembly;

FIG. 21B is a cross-sectional view taken from line 21B—21B of FIG. 10showing an arrangement of shift pins on a shift drum of the shiftassembly;

FIG. 21C is a flattened depiction of a cylindrical surface of a shiftdrum from the shift assembly of FIG. 10;

FIG. 22 is a perspective view of an exemplary shift pawl according toanother aspect of the present invention; and

FIGS. 23A–23C shows a side view of the rotation of an exemplary shiftdrum by the shift pawl of FIG. 22 during three phases of a downshiftoperation.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIGS. 2–23C, the present invention is directed to a sixspeed gear assembly and/or components related thereto for use in a sixspeed transmission case. Alternatively or in addition, the presentinvention is directly to a six speed gear assembly and/or componentsrelated thereto for retrofitting to a five speed transmission case.

FIG. 1 shows the major components of a stock Harley Davidson® five speedtransmission 8. Many of the smaller components of the transmission 8,which are well known to those skilled in the art, are not shown forclarity. The transmission 8 includes a stock Harley Davidson® five speedtransmission case 9. The transmission case 9 includes a central portion13, a first side wall 19 (hereinafter side wall 19), and a removablesecond side wall or trapdoor 21 (sometimes referred to as a bearinghousing assembly, and hereinafter referred to as trapdoor 21.) Thecentral portion 13, the side wall 19 and the trapdoor 21 together definea cavity 23. The central portion 13 also has an central portion opening15.

A first recess 25 in the side wall 19 receives a mainshaft case bearing27, and a second recess 29 in the side wall 19, adjacent to the firstrecess 25, receives a countershaft case bearing 31. The mainshaft casebearing 27 is pressed against a shoulder (not shown) of the first recess25 and held thereagainst by a snap ring (not shown). The countershaftcase bearing 31 is press fit in the second recess 29 of the side wall19.

A first recess 33 in the trapdoor 21 receives a mainshaft trapdoorbearing 35, and a second recess 37 in the trapdoor 21, adjacent to thefirst recess 33, receives a countershaft trapdoor bearing 39. Themainshaft trapdoor bearing 35 is pressed against a shoulder 111 of thefirst recess 33 and held thereagainst by a snap ring (not shown).Similarly, the countershaft trapdoor bearing 39 is pressed against ashoulder 113 of the second recess 37 and held thereagainst by a snapring (not shown).

FIG. 1 also shows a stock Harley Davidson® five speed gear assembly 41.The five speed gear assembly 41 includes a mainshaft 43 and acountershaft 45. The mainshaft 43 has mounted thereto, a mainshaft 5thgear 47, a mainshaft 2nd gear 51, a mainshaft 3rd gear 53, a mainshaft1st gear 55 and a mainshaft 4th gear 57. Similarly, the countershaft 45has mounted thereto, a countershaft 5th gear 59, a countershaft 2nd gear61, a countershaft 3rd gear 63, a countershaft 1st gear 65 and acountershaft 4th gear 67. Some of the components of the five speed gearassembly 41, such as split case bearings, retaining rings, thrustwashers, and spacers, are not shown for clarity.

To install the five speed gear assembly 41 into the five speedtransmission case 9, the mainshaft 43 and the countershaft 45 aresecured to the trapdoor 21, such as by hex nuts 69 that engage threadedsecond ends 121 and 123 of the mainshaft 43 and the countershaft 45,respectively. The mainshaft trapdoor bearing 35 supports the second endof mainshaft 43 and the countershaft trapdoor bearing 39 supports thesecond end of countershaft 64. The trapdoor 21, with the five speed gearassembly 41 secured thereto, is fastened to the transmission case 9 byconventional fasteners (not shown).

When the five speed gear assembly 41 is installed into the transmissioncase 9, an outer bearing surface 71 of the mainshaft 5th gear 47 issupported by the mainshaft case bearing 27. An outer splined portion 73of the mainshaft 5th gear 47 and the first end of mainshaft 43 protrudeoutside of the transmission case 9. The first end of the countershaft 45is supported by the countershaft case bearing 31.

FIG. 1 also shows a shifting assembly 75. The shifting assembly 75includes a shift drum 77 supported by first and second shift drumsupports 79 and 81. The shift drum 77 includes grooves 83, 85 and 87that for convenience have not been accurately depicted because they arewell known. Shift forks 91, 93, and 95 are mounted in and guided by theshift drum grooves 83, 85 and 87, respectively.

The first and second shift drum supports 79 and 81 are mounted to a topsurface 89 of the central portion 13 of the transmission case 9 byfasteners that extend through mounting collars 117 of the drum supports79 and 81 and into mounting holes 115. With the shift drum supports 79and 81 so mounted, the shift forks 91, 93 and 95 extend through centralportion opening 15 and into transmission case cavity 23.

Each shift fork 91, 93 and 95 is supported within the cavity 23 by ashift fork shaft 99, which is mounted between an opening 119 in a shiftfork shaft mounting flange 101, which extends downwardly from the topsurface 89 of the central portion 13 of the transmission case 9, and anopening 103 defined by the side wall 19 of the transmission case 9.

In operation, when a shifter rod lever 125 rotates in response to amotorcycle operator actuating a shift pedal (not shown), a shift pawl127 connected to the shifter rod lever 125 acts against shift pins 105on the shift drum 77, causing the shift drum 77 to rotate. As the shiftdrum 77 rotates, an interaction of a detent follower 107 with a detenttrack 109, mounted to the shift drum 77, biases the shift drum 77 topredetermined angular positions. The rotation of the shift drum 96 tothe predetermined angular positions causes one or more of shift forks91, 93, and 95 to move axially along shift fork shaft 99 by action ofthe shift drum grooves 83, 85 and 87, respectively. Movements of theshift forks 91, 93, and 95 cause corresponding axial movements of gearsalong the mainshaft 43 and/or along the countershaft 45, causing achange in the gear ratio of the five speed gear assembly 41. FIG. 2shows a six speed gear assembly 10 according to an exemplary embodimentof the invention. The six speed gear assembly 10 includes a mainshaft12, a mainshaft 4th gear 20, a 3–4 spline sleeve 22, a 3–4 shift ring24, a mainshaft 3rd gear 26, a mainshaft 1st gear 28, a mainshaft 2ndgear 30, a mainshaft 6th gear 32, a 5–6 shift ring 34, and a mainshaft5th gear 36. The six speed gear assembly 10 also includes a countershaft14, a countershaft 4th gear 38, a countershaft 3rd gear 40, countershaft1st gear 42, a 1–2 spline sleeve 44, a 1–2 shift ring 46, a countershaft2nd gear 48, a countershaft 6th gear 49 and a countershaft 5th gear 50.The exemplary six speed gear assembly 10 also includes split casebearings, retaining rings, thrust washers, and spacers, although, forclarity, not all these components are shown.

As shown in FIG. 2, the mainshaft 12 includes splined regions 16A, 16B,16C and 16D and bearing regions 18A, 18B, 18C and 18D. An exemplaryarrangement of the mainshaft gears on the mainshaft 12 and exemplarymainshaft gears are described below.

The mainshaft 4th gear 20 has teeth 58 that extend from a body portion52. The body portion 52 has a generally smooth central opening 54 and aplurality of radially spaced pockets 56 recessed therein (see also FIGS.5A–6B.) The central opening 54 is mounted on the bearings of a splitcage bearing 116, which in turn is rotatably mounted on the bearingregion 18A of the mainshaft 12. As such, the mainshaft 4th gear 20 isfree to rotate with respect to the mainshaft 12 (i.e. rotatably mountedto the mainshaft 12.) In an exemplary embodiment, the mainshaft 4th gear20 has a diametrical pitch of 12.7, 38 teeth and a thickness ofapproximately 0.661 inches.

The spline sleeve 22 is coupled to a splined region 16A of the mainshaft12. The spline sleeve 22 has external teeth 62 and internal teeth 60.The internal teeth 60 of the spline sleeve 22 mate with external teethon the splined region 16A of the mainshaft 12, enabling the splinesleeve 22 to rotate with the mainshaft 12 (i.e. the spline sleeve 22 isnon-rotatably mounted to the mainshaft 12.) In the exemplary embodiment,the spline sleeve 22 has a thickness of approximately 0.708 inches.

The 3–4 shift ring 24 (see also FIGS. 3A and 3B) is mounted insurrounding relation to the spline sleeve 22. The 3–4 shift ring 24 hasinternal teeth 64 that mesh with the external teeth 62 of the splinesleeve 22. As such, the 3–4 shift ring 24 rotates with the mainshaft 12(i.e. the 3–4 shift ring 24 is non-rotatably mounted to the mainshaft12.) The 3–4 shift ring 24 also includes a body portion 66 having afirst plurality of dogs 68A protruding from a first side of the body 66Aand a second plurality of dogs 68B protruding from a second side of thebody 66B. The body 66 also includes a circumferential shift fork groove70 radially extending therein.

The mainshaft 3rd gear 26 has teeth 72 that extend from a body portion74. The body portion 74 has a generally smooth central opening 76 and aplurality of radially spaced pockets 78 recessed therein (see also FIGS.5A–6B.) The central opening 76 is mounted on the bearings of a splitcage bearing 116, which in turn is rotatably mounted on the bearingregion 18B of the mainshaft 12. As such, the mainshaft 3rd gear 26 isfree to rotate with respect to the mainshaft 12 (i.e. rotatably mountedto the mainshaft 12.) In the exemplary embodiment, the mainshaft 3rdgear 26 has a diametrical pitch of 12, 32 teeth and a thickness ofapproximately 0.661 inches.

The 3–4 shift ring 24 is axially moveable with respect to the splinesleeve 22 into a neutral position, or one of two engaged positions. In afirst engaged position of the 3–4 shift ring 24 (see FIG. 18), thesecond plurality of dogs 68B engage pockets 56 in the mainshaft 4th gear20, enabling the mainshaft 4th gear 20 to rotate with the mainshaft 12(i.e. non-rotatably coupling the mainshaft 4th gear 20 to the mainshaft12.)

In a second engaged position of the 3–4 shift ring 24 (see FIG. 17), thefirst plurality of dogs 68A engage pockets 78 in the mainshaft 3rd gear26, enabling the mainshaft 3rd gear 26 to rotate with the mainshaft 12(i.e. non-rotatably coupling the mainshaft 3rd gear 26 to the mainshaft12.)

It should be noted that in the exemplary embodiment, the first engagedposition is opposite the second engaged position. Moreover, when the 3–4ring 24 is in the first engaged position, the first plurality of dogs68A are disengaged from the pockets 78 of the mainshaft 3rd gear 26.Similarly, when the 3–4 shift ring 24 is in the second engaged positionthe second plurality of dogs are disengaged from the pockets 56 of themainshaft 4th gear 20.

In the neutral position of the 3–4 shift ring 24, the first and secondplurality of dogs 68A and 68B are disengaged from the mainshaft 4th gear20 and the mainshaft 3rd gear 26, respectively, enabling the mainshaft4th gear 20 and the mainshaft 3rd gear 26 to each remain rotatablycoupled to the mainshaft 12.

The mainshaft 1st gear 28 is coupled to the splined region 16B of themainshaft 12. The mainshaft 1st gear 28 has external teeth 80 andinternal teeth 82. The internal teeth 82 of the mainshaft 1st gear 28mate with external teeth on the splined region 16B of the mainshaft 12,enabling the mainshaft 1st gear 28 to rotate with the mainshaft 12 (i.e.the mainshaft 1st gear 28 is non-rotatably mounted on the mainshaft 12.)In the exemplary embodiment, the mainshaft 1st gear 28 has a diametricalpitch of 10, 18 teeth and a thickness of approximately 0.761 inches.

The mainshaft 2nd gear 30 is coupled to the splined region 16C of themainshaft 12. The mainshaft 2nd gear 30 has external teeth 84 andinternal teeth 86. The internal teeth 86 of the mainshaft 2nd gear 30mate with external teeth on the splined region 16C of the mainshaft 12,enabling the mainshaft 2nd gear 30 to rotate with the mainshaft 12 (i.e.the mainshaft 2nd gear 30 is non-rotatably mounted on the mainshaft 12.)In the exemplary embodiment, the mainshaft 2nd gear 30 has a diametricalpitch of 12, 27 teeth and a thickness of approximately 0.661 inches.

The mainshaft 6th gear 32 has teeth 88 that extend from a body portion90. The body portion 90 has a generally smooth central opening 92 and aplurality of radially spaced pockets 94 recessed therein (see also FIGS.5A–6B.) The central opening 92 is mounted on the bearings of a splitcage bearing 116, which in turn is rotatably mounted on the bearingregion 18C of the mainshaft 12. As such, the mainshaft 6th gear 32 isfree to rotate with respect to the mainshaft 12 (i.e. rotatably mountedto the mainshaft 12.) In the exemplary embodiment, the mainshaft 6thgear 32 has a diametrical pitch of 12, 40 teeth and a thickness ofapproximately 0.661 inches.

The 5–6 shift ring 34 (see also FIGS. 4A and 4B) is mounted insurrounding relation to the splined region 16D of the mainshaft 12. The5–6 shift ring 34 has internal teeth 96 that mesh with external teeth onsplined region 16D of the mainshaft 12, enabling the 5–6 shift ring 34to rotate with the mainshaft 12 (i.e. the 5–6 shift ring 34 isnon-rotatably mounted on the mainshaft 12.) The 5–6 shift ring 34 alsoincludes a body portion 98 having a first plurality of dogs 100Aprotruding from a first side of the body 98A and a second plurality ofdogs 100B protruding from a second side of the body 98B. The body 98also includes a circumferential shift fork groove 102 radially extendingtherein.

The mainshaft 5th gear 36 has teeth 118 that extend from a body portion120. The body portion 120 has a generally smooth central opening 122 anda plurality of radially spaced pockets 124. Although, in the depictedembodiment, the pockets 124 extend into the central opening 122, it isalso contemplated that the pockets 124 may be formed in the body portion118 without extending into the central opening 122. The central opening122 is mounted on the bearings of a split cage bearing 116, which inturn is rotatably mounted on the bearing region 18D of the mainshaft 12.As such, the mainshaft 5th gear 36 is free to rotate with respect to themainshaft 12 (i.e. rotatably mounted on the mainshaft 12.) In oneexemplary embodiment, the mainshaft 5th gear 36 is a stock HarleyDavidson® mainshaft 5th gear. In one embodiment, an output gear 360 isintegrally formed with the mainshaft 5th gear 36.

The 5–6 shift ring 34 is axially moveable with respect to the splinedregion 16D of the mainshaft 12 into a neutral position, or one of twoengaged positions. In a first engaged position of the 5–6 shift ring 34(see FIG. 20), the second plurality of dogs 100B engage pockets 94 inthe mainshaft 6th gear 32, enabling the mainshaft 6th gear 32 to rotatewith the mainshaft 12 (i.e. non-rotatably coupling mainshaft 6th gear 32to the mainshaft 12.)

In a second engaged position of the 5–6 shift ring 34 (see FIG. 19), thefirst plurality of dogs 100A engage pockets 124 in the mainshaft 5thgear 36, enabling the mainshaft 5th gear 36 to rotate with the mainshaft12 (i.e. non-rotatably coupling mainshaft 5th gear 36 to the mainshaft12.)

It should be noted that in the exemplary embodiment, the first engagedposition is opposite the second engaged position. Moreover, when the 5–6shift ring 34 is in the first engaged position the first plurality ofdogs 100A are disengaged from the pockets 124 of the mainshaft 5th gear36. Similarly, when the 5–6 shift ring 34 is in the second engagedposition the second plurality of dogs 100B are disengaged from thepockets 94 of the mainshaft 6th gear 32.

In the neutral position of the 5–6 shift ring 34, the first and secondplurality of dogs 100A and 100B are disengaged from the mainshaft 5thgear 32 and the mainshaft 6th gear 36, respectively, enabling themainshaft 5th gear 32 and the mainshaft 6th gear 36 to each remainrotatably coupled to the mainshaft 12.

As shown in FIG. 2, the countershaft 14 includes splined regions 15A,15B, 15C and 15D and bearing regions 17A and 17B. An exemplaryarrangement of the countershaft gears on the countershaft 14 andexemplary countershaft gears are described below.

The countershaft 4th gear 38 is coupled to splined region 15A of thecountershaft 14. The countershaft 4th gear 38 has external teeth 104 andinternal teeth 106. The internal teeth 106 of the countershaft 4th gear38 mate with external teeth on the splined region 15A of thecountershaft 14, enabling the countershaft 4th gear 38 to rotate withthe countershaft 14 (i.e. the countershaft 4th gear 38 is non-rotatablymounted on the countershaft 14.) In the exemplary embodiment, thecountershaft 4th gear 38 has a diametrical pitch of 12.7, 25 teeth and athickness of approximately 0.661 inches.

The countershaft 3rd gear 40 is coupled to splined region 15B of thecountershaft 14. The countershaft 3rd gear 40 has external teeth 84 andinternal teeth 86. The internal teeth 86 of the countershaft 3rd gear 40mate with external teeth on the splined region 15B of the countershaft14, enabling the countershaft 3rd gear 40 to rotate with thecountershaft 14 (i.e. the countershaft 3rd gear 40 is non-rotatablymounted on the countershaft 14.) In an exemplary embodiment, thecountershaft 3rd gear 40 has a diametrical pitch of 12, 27 teeth and athickness of approximately 0.661 inches.

The countershaft 1st gear 42 has teeth 108 that extend from a bodyportion 110. The body portion 110 has a generally smooth central opening112 and a plurality of radially spaced pockets 114 recessed therein (seealso FIGS. 5A–6B.) The central opening 112 is mounted on the bearings ofa split cage bearing 116, which in turn is rotatably mounted on thebearing region 17A of the countershaft 14. As such, the countershaft 1stgear 42 is free to rotate with respect to the countershaft 14 (i.e.rotatably mounted on the countershaft 14.) In the exemplary embodiment,the countershaft 1st gear 42 has a diametrical pitch of 10, 31 teeth anda thickness of approximately 0.661 inches.

The spline sleeve 44 is coupled to splined region 15C of thecountershaft 14. The spline sleeve 22 has external teeth 62 and internalteeth 60. The internal teeth 60 of the spline sleeve 44 mate withexternal teeth on the splined region 15C of the countershaft 14,enabling the spline sleeve 44 to rotate with the countershaft 14 (i.e.the spline sleeve 44 is non-rotatably mounted to the countershaft 14.)In the exemplary embodiment, the spline sleeve 44 has a thickness ofapproximately 0.708 inches.

The 1–2 shift ring 46 (see also FIGS. 3A and 3B) is coupled to thespline sleeve 44. The 1–2 shift ring 46 has internal teeth 64 that meshwith the external teeth 62 of the spline sleeve 44. As such, the 1–2shift ring 46 rotates with the countershaft 14 (i.e. the 1–2 shift ring46 is non-rotatably mounted on the countershaft 14.) The 1–2 shift ring46 also includes a body portion 66 having a first plurality of dogs 68Aprotruding from a first side of the body 66A and a second plurality ofdogs 68B protruding from a second side of the body 66B. The body 66 alsoincludes a circumferential shift fork groove 70 radially extendingtherein.

The countershaft 2nd gear 48 has teeth 72 that extend from a bodyportion 74. The body portion 74 has a generally smooth central opening76 and a plurality of radially spaced pockets 78 recessed therein (seealso FIGS. 5A–6B.) The central opening 76 is mounted on the bearings ofa split cage bearing 116, which in turn is rotatably mounted on thebearing region 17B of the countershaft 14. As such, the countershaft 2ndgear 48 is free to rotate with respect to the countershaft 14 (i.e.rotatably mounted on the countershaft 14.) In an exemplary embodiment,the countershaft 2nd gear 48 has a diametrical pitch of 12, 32 teeth anda thickness of approximately 0.661 inches.

The 1–2 shift ring 46 is axially moveable with respect to the splinesleeve 44 into a neutral position, or one of two engaged positions. In afirst engaged position of the 1–2 shift ring 46 (see FIG. 15), thesecond plurality of dogs 68B engage pockets 114 in the countershaft 1stgear 42, enabling the countershaft 1st gear 42 to rotate with thecountershaft 14 (i.e. non-rotatably coupling the countershaft 1st gear42 to the countershaft 14.).

In a second engaged position of the 1–2 shift ring 46 (see FIG. 16), thefirst plurality of dogs 68A engage pockets 78 in the countershaft 2ndgear 48, enabling the countershaft 2nd gear 48 to rotate with thecountershaft 14 (i.e. non-rotatably coupling the countershaft 2nd gear48 to the countershaft 14.).

It should be noted that in the exemplary embodiment, the first engagedposition is opposite the second engaged position. Moreover, when the 1–2shift ring 46 is in the first engaged position the first plurality ofdogs 68A are disengaged from the pockets 78 of the mainshaft second gear48. Similarly, when the 1–2 shift ring 46 is in the second engagedposition the second plurality of dogs 68B are disengaged from thepockets 114 of the mainshaft first gear 42.

In the neutral position of the 1–2 shift ring 46, the first and secondplurality of dogs 68A and 68B are disengaged from the countershaft 1stgear 42 and the countershaft 2nd gear 48, respectively, enabling thecountershaft 1st gear 42 and the countershaft 2nd gear 48 to each remainrotatably coupled to the countershaft 14.

In one embodiment, the countershaft 6th gear 49 is fixedly attached orintegrally formed with the countershaft 14, enabling the countershaft6th gear 49 to rotate with the countershaft 14 (i.e. the countershaft6th gear 49 is non-rotatably coupled to the countershaft 14.) In anexemplary embodiment, the countershaft 6th gear 49 has a diametricalpitch of 12, 19 teeth and a thickness of approximately 0.671 inches.

The countershaft 5th gear 50 is coupled to splined region 15D of thecountershaft 14. The countershaft 5th gear 50 has external teeth 126 andinternal teeth 128. The internal teeth 128 of the countershaft 5th gear50 mate with external teeth on the splined region 15D of thecountershaft 14, enabling the countershaft 5th gear 50 to rotate withthe countershaft 14 (i.e. the countershaft 5th gear 50 is non-rotatablymounted on the countershaft 14.) In one embodiment, the mainshaft 5thgear 36 is a stock Harley Davidson® mainshaft 5th gear.

In one embodiment, each of the mainshaft gears 1st through 6th(mainshaft gears 20, 26, 28, 30, 32, and 36, respectively) cannot moveaxially relative to the mainshaft 12 and each of the countershaft gears1st through 6th (countershaft gears 38, 40, 42, 48, 49, and 50,respectively) cannot move axially relative to the countershaft 14. Thisconfiguration allows each mainshaft gear to mesh in 100% gear meshengagement with its corresponding countershaft gear as shown in FIG. 9.

In one embodiment, the mainshaft gears 1st through 5th (mainshaft gears20, 26, 28, 30, and 36, respectively) each have the same gear ratios asstock Harley Davidson® mainshaft gears 1st through 5th, and themainshaft 6th gear has a gear ratio of approximately 0.885 to 1. In oneembodiment, the mainshaft gears 1st through 5th (mainshaft gears 20, 26,28, 30, and 36, respectively) each have generally the same thickness asstock Harley Davidson® mainshaft gears 1st through 5th. In anotherembodiment, the mainshaft gears 1st through 5th (mainshaft gears 20, 26,28, 30, and 36, respectively) are each approximately 0.010 to 0.060inches greater in thickness than the corresponding stock HarleyDavidson® mainshaft gears 1st through 5th.

In one embodiment, any or all of the following gears: (the mainshaft 4thgear 20, the mainshaft 3rd gear 26, the mainshaft 6th gear 32, themainshaft 5th gear 36, the countershaft 1st gear 42 and the countershaft2nd gear 48) may have the general pocket configuration and the generalinternal diameter configuration of a first exemplary gear 298 as shownin FIGS. 5A–5B or the general pocket configuration and the generalinternal diameter configuration of a second exemplary gear 306 as shownin FIGS. 6A–6B.

As shown in FIGS. 5A–5B, the first exemplary gear 298 has a body portion300 with a generally smooth central opening 302 extending therethroughand a plurality of radially spaced pockets 304 recessed therein. Thefirst exemplary gear 298 includes five pockets 304 equally spaced abouta radius of the first exemplary gear 298. Each pocket 304 is generallytrapezoid shaped and is recessed into the body portion 300 to a depth ofapproximately 0.185 inches. However, in other embodiments any number ofpockets 304 having any appropriate shape may be used, and each pocket304 may be recessed to any appropriate depth into the body portion 300or may even extend entirely through the body portion 300. In theconfiguration of FIGS. 5A–5B, each side of the perimeter of each pocket304 is defined by the body portion 300. As such, when a dog is insertedinto a corresponding one of the pockets 304, the pocket 304 has a largebearing surface for the dog to bear against.

As shown in FIGS. 6A–6B, the second exemplary gear 306 has a bodyportion 308 with a generally smooth central opening 310 extendingtherethrough and a plurality of radially spaced pockets 312 recessedtherein. The second exemplary gear 306 includes five pockets 312 equallyspaced about a radius of the second exemplary gear 310 and extendinginto the central opening 310. Each pocket 312 is generally trapezoidshaped and is recessed into the body portion 308 to a depth ofapproximately 0.185 inches. However, in other embodiments any number ofpockets 312 having any appropriate shape may be used, and each pocket312 may be recessed to any appropriate depth into the body portion 308or may even extend entirely through the body portion 308.

When the six speed gear assembly 10 is assembled, as shown for examplein FIG. 9, the mainshaft 12 and the countershaft 14 may each be mountedto a conventional trapdoor, such as the trapdoor 21 of FIG. 1.Alternatively, when the six speed gear assembly 10 is assembled, themainshaft 12 and the countershaft 14 may each be mounted to a trapdoor130 (sometimes referred to as a bearing housing assembly) according toone aspect of the present invention (as shown for example in FIGS. 2,7A–7B and 9).

As shown in FIGS. 7A–7B, the trapdoor 130 includes a first recess 132that receives the mainshaft trapdoor bearing 35 (see FIG. 2) and asecond recess 134 that receives the countershaft trapdoor bearing 39(see FIG. 2). The mainshaft trapdoor bearing 35 is pressed against ashoulder 136 of the first recess 132 and held thereagainst by a snapring (not shown) disposed in snap ring groove 138. Similarly, thecountershaft trapdoor bearing 39 is pressed against a shoulder 140 ofthe second recess 134 and held thereagainst by a snap ring (not shown)disposed in snap ring groove 142.

A third recess 144 extends in surrounding relation to the first andsecond recesses 132 and 134. The third recess 144 is substantially ovalshaped, having a length L of a sufficient size to accommodate a meshedgear coupling of one of the mainshaft gears and its correspondingcountershaft gear. For example, in one embodiment, the length L of thethird recess 144 is of a sufficient size to accommodate the meshedcoupling of the mainshaft 4th gear 20 and the countershaft 4th gear 38.In this embodiment, the length L of the third recess 144 isapproximately 5.73 inches.

The depth of the third recess 144 is dimensioned to receive at least aportion of the thicknesses of one of the mainshaft gears and itscorresponding countershaft gear. For example, in one embodiment, thedepth of the third recess 144 is dimensioned to receive at least aportion of the thicknesses of each of the mainshaft 4th gear 20 and thecountershaft 4th gear 38. In one embodiment, the depth of the thirdrecess 144 is approximately 0.565 inches.

The third recess 144 of the trapdoor 130 allows for a six speed gearassembly to be mounted in the stock Harley Davidson® five speedtransmission case 9 or a modified stock transmission case 9′ (as shownin FIG. 9 and described in detail below) without modifying the outerdimensions of the stock Harley Davidson® five speed transmission case 9or 9′. The third recess 144 of the trapdoor 130 also allows for a sixspeed gear assembly to be mounted in a stock Harley Davidson® five speedtransmission case 9 or the modified stock transmission case 9′ withoutdecreasing the thickness of the gears compared to the thickness of thegears in a stock Harley Davidson® five speed gear assembly.

A six speed gear assembly can be mounted in the stock Harley Davidson®five speed transmission case 9 or the modified stock transmission case9′ without the use of the third recess 144 of the trapdoor 130; however,such an arrangement would likely require decreasing the thickness of thegears compared to the thickness of the gears in a stock Harley Davidson®five speed gear assembly. Such a decrease in the thickness of the gearsincreases the risk of a fracture of one or more of the gears.

As previously stated, the third recess 144 overlaps both the first andsecond recesses 132 and 134. The first recess 132 includes a firstopening 146 that extends into the third recess 144 and across the widthof the trapdoor 130 to receive the mainshaft 12. Similarly, the secondrecess 134 includes a second opening 148 that extends into the thirdrecess 144 and across the width of the trapdoor 130 to receive thecountershaft 14.

Viewing FIGS. 7A–7B and 9 together, to secure the six speed gearassembly 10 to the trapdoor 130, the mainshaft 12 is inserted into thefirst opening 146 of the trapdoor 130 until a shoulder 150 of themainshaft abuts an interior wall 154 of the third recess 144. Thisallows a bearing surface 156 of the mainshaft 12 to be supported by themainshaft trapdoor bearing 35 and a threaded end 158 of the mainshaft 12to extend from an opening in the mainshaft trapdoor bearing 35. The hexnut 69, or another similar fastener, threadably engages the threaded end158 of the mainshaft to secure the mainshaft 12 to the trapdoor 130.

Similarly, the countershaft 14 is inserted into the second opening 148of the trapdoor 130 until a shoulder 160 of the countershaft 14 abutsthe interior wall 154 of the third recess 144. This allows a bearingsurface 162 of the countershaft 14 to be supported by the countershafttrapdoor bearing 39 and a threaded end 164 of the countershaft 14 toextend from an opening in the countershaft trapdoor bearing 39. The hexnut 69, or another similar fastener, threadably engages the threaded end164 of the countershaft 14 to secure the countershaft 14 to the trapdoor130.

With the exemplary six speed gear assembly 10 secured to the trapdoor130 as described above, a mainshaft gear and its correspondingcountershaft gear, such as the mainshaft 4th gear 20 and thecountershaft 4th gear 38, are each substantially disposed within thethird recess 144 of the trapdoor 130. In one embodiment, a mainshaftgear and its corresponding countershaft gear, such as the mainshaft 4thgear 20 and the countershaft 4th gear 38, are disposed within thetrapdoor and are substantially flush with or extend slightly from an endsurface 166 of the trapdoor 130, which defines the third recess 144.

In one embodiment, such as that shown in FIG. 7A, a speedo sensor 168,for example a stock Harley Davidson® magnetic speedo sensor, is mountedin an angled bore 181 formed in a sidewall of the trapdoor 130, adjacentto the third recess 144 of the trapdoor 130. As such, when the six speedgear assembly 10 is mounted to the trapdoor 130, the speedo sensor 168is disposed in close proximity to one of the two gears that are mountedwithin the third recess 144 of the trapdoor 130.

The speedo sensor 168 counts the number of gear teeth per unit time ofthe gear that rotates in close proximity to it. From this calculation,the speed of the motorcycle, to which the six speed gear assembly 10 isattached, is determined. In one embodiment, the mainshaft 4th gear 20 ismounted within the third recess 144 of the trapdoor such that it isdisposed in close proximity to the speedo sensor 168. In thisembodiment, the speedo sensor 168 determines the rotational speed of themainshaft 4th gear 20.

Since the stock Harley Davidson® five speed transmission 8 also includesa speedo sensor that measures the rotational speed of the stock HarleyDavidson® mainshaft 4th gear and calculates the speed of the motorcycleto which the transmission 8 is attached based on the measured rotationalspeed of the stock Harley Davidson® mainshaft 4th gear, it isadvantageous when retrofitting to the exemplary embodiment six speedgear assembly 10 to a stock Harley Davidson® five speed transmissioncase to position the mainshaft 4th gear 20 of the six speed gearassembly 10 in close proximity to the speedo sensor 168 so thatrecalibration of the speedo sensor 168 is not required in order todetermine the speed of the motorcycle to which the six speed gearassembly 10 is attached.

As shown in FIGS. 7A–7B, the trapdoor 130 includes a base 170. The base170 includes the end surface 166 of the trapdoor 130. The trapdoor 130may be mounted to the stock Harley Davidson® five speed transmissioncase 9 of FIG. 1; or as shown in FIG. 9, the trapdoor 130 may be mountedto a modified stock Harley Davidson® five speed transmission case 9′, byfasteners (not shown) that extend through openings 172 in the base 170of the trapdoor 130 and attach to a mounting location on the modifiedstock transmission case 9′ to secure the trapdoor 130 thereto. Themodification of the stock transmission case 9 is described in detailbelow.

As shown in FIGS. 7A–7B, adjacent to the base 170 of the trapdoor 130 isa first protruding surface 174 that axially extends from the base 170 ofthe trapdoor 130 and includes fastener openings 176B for securing thetrapdoor 130 to the transmission case 9 or 9′ and fastener openings 176for securing an end cover 178 (as shown for example in FIGS. 2, 8A–8B,and 9 and sometimes referred to as a clutch release cover) to thetrapdoor 130. The first protruding surface 174 includes a face surface174A that is directed oppositely from the end surface 166 of the base170.

Adjacent to the first protruding surface 174 of the trapdoor 130 is asecond protruding surface 180 that axially extends from the firstprotruding surface 174 of the trapdoor 130 and laterally extends fromthe first and second recesses 132 and 134 of the trapdoor 130. Thesecond protruding surface 180 is generally oval shaped with a pluralityof ears 182 extending therefrom. The second protruding surface 180 alsoincludes a shift fork shaft opening 236, discussed below.

FIGS. 8A–8B show the end cover 178. The end cover 178 includes a recess184 (drawn in bold for clarity) and fastener openings 186 and 186B.Viewing FIGS. 7A–9 together, the end cover 178 is mounted to thetrapdoor 130 over the first and second recesses 132 and 134 of thetrapdoor 130 by placing the recess 184 of the end cover 178 over thesecond protruding surface 180 of the trapdoor 130, such that an interiorsurface 188 of the recess 184 of the end cover 178 abuts the facesurface 174A of the first protruding surface 174 of the trapdoor 130.

The recess 184 of the end cover 178 has the same general shape and sizeof the second protruding surface 180 of the trapdoor 130 such that thesecond protruding surface 180 of the trapdoor 130 mates with the recess184 of the end cover 178 in a manner that prevents rotational movementof the end cover 178 with respect to the trapdoor 130. For example, inthe depicted embodiment of FIGS. 8A–8B, the recess 184 of the end cover178 is generally oval shaped with a plurality of ears 190 extendingtherefrom that substantially mimic the shape and size of the ears 182 ofthe second protruding surface 180 of the trapdoor 130. However, in otherembodiments the second protruding surface 180 of the trapdoor 130 andthe recess 184 of the end cover 178 may any other appropriate shape andneed not be of the same general shape and/or the same general size aslong as a rotational movement of the end cover 178 with respect to thetrapdoor 130 is prevented when the second protruding surface 180 of thetrapdoor 130 is inserted into the recess 184 of the end cover 178.

In essence, the second protruding surface 180 provides a guide forguiding the end cover 178 in the appropriate position with respect tothe trapdoor 130, preventing a rotation of the end cover 178 relative tothe trapdoor 130 and aligning the appropriate fastener holes that allowfor a coupling of the end cover 178 to the trapdoor 130.

When the recess 184 of the end cover 178 receives the second protrudingsurface 180 of the trapdoor 130, the fastener openings 186 and 186B ofthe end cover 178 are automatically aligned with the fastener openings176 and 176B of the trapdoor 130. The end cover 178 is then mounted tothe trapdoor 130 by inserting fasteners (not shown) into and through thefastener openings 186 of the end cover 178 and engaging the fasteneropenings 176 of the trapdoor 130, which in one embodiment are internallythreaded.

The end cover 178 and the trapdoor 130 are mounted to the stock HarleyDavidson® five speed transmission case 9 of FIG. 1, for example, byinserting fasteners (not shown) into and through the fasteners openings186B of the end cover 178 and the fasteners opening 176B of the trapdoor130 and engaging the fasteners (not shown) with openings in thetransmission case 9. The end cover 178 and the trapdoor 130 are mountedto the modified stock transmission case 9′ in a similar fashion.

FIG. 10 shows a shifting assembly 192. The shifting assembly 192includes a shift drum 194 supported by first and second shift drumsupports 210 and 212; a detent track 228 adjacent to one side of theshift drum 194; and a generally hexagonally shaped shift pin plate 362adjacent to an opposite side of the shift drum 194. The shift pin plate362 supports a plurality of shift pins 224. The shift drum 194 includesshift drum grooves 196A–196D recessed therein. A 3–4shift fork 198 (seealso FIGS. 11A–11B) includes a pin 200 that rides within and is guidedby the 3–4 shift drum groove 196A. The 3–4 shift fork 198 also includesa generally semi-circular shaped fork arm 230 that mates with the shiftfork groove 70 in the 3–4 shift ring 24 (see also FIGS. 2 and 3A–3B.)

A 1–2 shift fork 202 (see also FIGS. 12A–12B) includes a pin 204 thatrides within and is guided by 1–2 shift drum groove 196C. The 1–2 shiftfork 202 also includes and a generally semi-circular shaped fork arm 232that mates with the shift fork groove 70 in the 1–2 shift ring 46 (seealso FIGS. 2 and 3A–3B.).

A 5–6 shift fork 206 (see also FIGS. 13A–13B) includes a pin 208 thatrides within and is guided by 5–6 shift drum groove 196D. The 5–6 shiftfork 206 also includes a generally semi-circular shaped fork arm 234that mates with the shift fork groove 102 in the 5–6 shift ring 34 (seealso FIGS. 2 and 4A–4B.).

A neutral switch (not shown) rides within the neutral track shift drumgroove 196B for detecting a neutral gear position of the six speed gearassembly 10 (as shown in FIG. 14.) In one embodiment, the neutral trackshift drum groove 196 b is approximately 0.44 inches wide. The increasedwidth of the neutral track shift drum groove 196 b similar to the stockHarley Davidson® neutral track shift drum groove allows for a greatervariety of neutral switches to be used to detect the neutral gearposition.

As shown in FIG. 9, the first and second shift drum supports 210 and 212are mounted to the top surface 89 of the central portion 13 of themodified stock transmission case 9′ by fasteners (not shown) that extendthrough mounting collars 214 of the drum supports 210 and 212 and intomounting holes 115 of the modified stock transmission case 9′. With theshift drum supports 210 and 212 so mounted, the shift forks 198, 202 and206 extend through central portion opening 15 and into transmission casecavity 23.

All of the shift forks 198, 202 and 206 are supported within the cavity23 by a shift fork shaft 216, which extends through openings 218, 220and 222, respectively, in the shift forks 198, 202 and 206 (openings218, 220 and 222 are as shown in FIGS. 11A, 12A and 13A, respectively.)The shift fork shaft 216 is mounted to the modified stock transmissioncase 9′ as described below.

As shown in FIG. 9, in operation, when a shifter rod lever 125 rotatesin response to a motorcycle operator actuating a shift pedal (notshown), a shift pawl 258 (described below) correspondingly rotates theshift pins 224 of the shift drum 192, causing the shift drum 192 torotate. As the shift drum 192 rotates, an interaction of a detentfollower 226 with the detent track 228, which is mounted on the shiftdrum 192, biases the shift drum 192 to predetermined angular positions.As shown, the detent follower 226 has a first end 226A pivotallysupported by a portion 229 of the first shift drum support 210 and asecond end 226B having a roller 227 biased into contact with the detenttrack 228. The rotation of the shift drum 192 to the predeterminedangular positions causes one or more of shift forks 198, 202 and 206 tomove axially along shift fork shaft 216 by guiding action of the shiftdrum grooves 196A, 196C and 196D, respectively.

Axial movements of the 3–4 shift fork 198 causes corresponding axialmovements of the 3–4 shift ring 24. Similarly, axial movements of the1–2 shift fork 202 causes corresponding axial movements of the 1–2 shiftring 46. Also similarly, axial movements of the 5–6 shift fork 206causes corresponding axial movements of the 5–6 shift ring 34.

In an exemplary embodiment, in order to mount the shift fork shaft 216to the stock Harley Davidson® five speed transmission case 9 of FIG. 1,the shift fork shaft mounting flange 101 of the transmission case 9 ofFIG. 1 must be removed as shown in the modified stock transmission case9′ of FIG. 9), otherwise the shift fork shaft mounting flange 101 wouldinterfere with the axial movements of the 3–4 shift fork 198. In analternative embodiment, rather than modifying an existing transmissioncase, a new transmission case is used.

In the embodiment of FIG. 9, the shift fork shaft mounting flange 101 isremoved and the shift fork shaft 216 is mounted between the shift forkshaft opening 236 in the trapdoor 130 and the shift fork shaft opening103 in the side wall 19 of the modified stock transmission case 9′. Inone exemplary embodiment, a template is provided for defining theportion of the shift fork shaft mounting flange 101 to be removed. Inthe depicted embodiment, when the shift fork shaft mounting flange 101is removed a generally semi-circular opening 231 is formed, having asize sufficient for allowing the passage of the 3–4 shift fork 198riding on the shift fork shaft 216.

When the trapdoor 130 is attached to the modified stock transmissioncase 9′, the shift fork shaft opening 236 in the trapdoor 130 is alignedwith both the shift fork shaft opening 103 in the side wall 19 of themodified stock transmission case 9′ and with the location of the opening119 of the shift fork shaft mounting flange 101 prior to the removal andof the fork shaft mounting flange 101. As such, the position of theshift drum 194 relative to the modified stock transmission case 9′ isunchanged from that of the stock Harley Davidson® five speedtransmission 8. In one embodiment, one end of the shift fork shaft 216threadingly engages the shift fork shaft opening 236 in the trapdoor 130and another end of the shift fork shaft 216 fits snugly within the shiftfork shaft opening 103 in the side wall 19 of the modified stocktransmission case 9′.

As shown in FIGS. 11A–11B, the 3–4 shift fork 198 includes an elongatedgenerally horizontal arm 238. The pin 200 extends generallyperpendicularly and generally upwardly from the horizontal arm 238 andthe fork arm 230 extends generally perpendicularly and generallydownwardly from the horizontal arm 238. When the 3–4 shift fork 198 isused on the modified stock transmission case 9′, the elongated length ofthe horizontal arm 238 allows the pin 200 of the 3–4 shift fork 198 toextend through the central portion opening 15 of the modified stocktransmission case 9′ even when the fork arm 230 of the 3–4 shift fork198 is in close proximity to the trapdoor 130 (such as when the fork arm230 of the 3–4 shift fork 198 has moved the 3–4 shift ring 24 intoengagement with the mainshaft 4th gear 20.) The elongated length of thehorizontal arm 238 of the 3–4 shift fork 198 allows the exemplary sixspeed gear assembly 10 to be incorporated into the modified stocktransmission case 9′.

When the 3–4 shift fork 198 is used with the six speed gear assembly 10and the 3–4 shift ring 24 is engaged with the mainshaft 4th gear 20, theelongated length of the horizontal arm 238 also allows the 3–4 shiftfork 198 to straddle or extend over each of the 3–4 shift ring 24 (andits underlying spline sleeve 22), the mainshaft 3rd gear 26, themainshaft 1st gear 28, and a portion of the 1–2 shift ring 46.

When the 3–4 shift fork 198 is used with the six speed gear assembly 10and the 3–4 shift ring 24 is engaged with the mainshaft 3rd gear 26, theelongated length of the horizontal arm 238 also allows the 3–4 shiftfork 198 to straddle or extend over each of the 3–4 shift ring 24 (and aportion of its underlying spline sleeve 22), the mainshaft 3rd gear 26,the mainshaft 1st gear 28 and the second side 66B of the 1–2 shift ring46, such that an oil slot 238A in the shift fork 198 is disposed abovethe second side 66B of the 1–2 shift ring 46. In one exemplaryembodiment, the horizontal arm 238 is approximately 2.01 inches inlength.

As shown in FIGS. 14–20, when the six speed gear assembly 10 isassembled, each mainshaft gear meshes with a corresponding countershaftgear. FIG. 14 shows the six speed gear assembly 10 in the neutral gearposition. When the six speed gear assembly 10 is in the neutral gearposition, each shift ring 24, 34, and 46 is in its neutral position(described above) and hence torque is not transferred between themainshaft 12 and countershaft 14 since each meshed gear pairing includesone gear that is rotatably coupled to its corresponding shaft and onegear that is non-rotatably coupled to its corresponding shaft.

FIG. 15 shows the six speed gear assembly 10 in the 1st gear position.When the six speed gear assembly 10 is in the 1st gear position, the 3–4shift ring 24 and the 5–6 shift ring 34 are each in their neutralpositions, while the 1–2 shift ring 46 is engaged with the countershaft1st gear 42, which causes the countershaft 1st gear 42 to benon-rotatably coupled to the countershaft 14. Since the mainshaft 1stgear 28 is non-rotatably coupled to the mainshaft 12, torque istransferred between the mainshaft 12 and the countershaft 14 by themainshaft 1st gear 28 and the countershaft 1st gear 42; and since thecountershaft 5th gear 50 is non-rotatably coupled to the countershaft14, torque is transferred to the mainshaft 5th gear 36 as shown by arrow240. Torque is then transferred from the output gear 360 of themainshaft 5th gear 36 to a drive belt or drive chain (not shown) todrive a rear wheel of the motorcycle.

FIG. 16 shows the six speed gear assembly 10 in the 2nd gear position.When the six speed gear assembly 10 is in the 2nd gear position, the 3–4shift ring 24 and the 5–6 shift ring 34 are each in their neutralpositions, while the 1–2 shift ring 46 is engaged with the countershaft2nd gear 48, which causes the countershaft 2nd gear 48 to benon-rotatably coupled to the countershaft 14. Since the mainshaft 2ndgear 30 is non-rotatably coupled to the mainshaft 12, torque istransferred between the mainshaft 12 and the countershaft 14 by themainshaft 2nd gear 30 and the countershaft 2nd gear 48; and since thecountershaft 5th gear 50 is non-rotatably coupled to the countershaft14, torque is transferred to the mainshaft 5th gear 36 as shown by arrow242. Torque is then transferred from the output gear 360 of themainshaft 5th gear 36 to the drive belt to drive the rear wheel of themotorcycle.

FIG. 17 shows the six speed gear assembly 10 in the 3rd gear position.When the six speed gear assembly 10 is in the 3rd gear position, the 1–2shift ring 46 and the 5–6 shift ring 34 are each in their neutralpositions, while the 3–4 shift ring 24 is engaged with the mainshaft 3rdgear 26, which causes the mainshaft 3rd gear 26 to be non-rotatablycoupled to the mainshaft 12. Since the countershaft 3rd gear 40 isnon-rotatably coupled to the countershaft 14, torque is transferredbetween the mainshaft 12 and the countershaft 14 by the mainshaft 3rdgear 26 and the countershaft 3rd gear 40; and since the countershaft 5thgear 50 is non-rotatably coupled to the countershaft 14, torque istransferred to the mainshaft 5th gear 36 as shown by arrow 244. Torqueis then transferred from the output gear 360 of the mainshaft 5th gear36 to the drive belt to drive the rear wheel of the motorcycle.

FIG. 18 shows the six speed gear assembly 10 in the 4th gear position.When the six speed gear assembly 10 is in the 4th gear position, the 1–2shift ring 46 and the 5–6 shift ring 34 are each in their neutralpositions, while the 3–4 shift ring 24 is engaged with the mainshaft 4thgear 20, which causes the mainshaft 4th gear 20 to be non-rotatablycoupled to the mainshaft 12. Since the countershaft 4th gear 38 isnon-rotatably coupled to the countershaft 14, torque is transferredbetween the mainshaft 12 and the countershaft 14 by the mainshaft 4thgear 20 and the countershaft 4th gear 38; and since the countershaft 5thgear 50 is non-rotatably coupled to the countershaft 14, torque istransferred to the mainshaft 5th gear 36 as shown by arrow 246. Torqueis then transferred from the output gear 360 of the mainshaft 5th gear36 to the drive belt to drive the rear wheel of the motorcycle.

FIG. 19 shows the six speed gear assembly 10 in the 5th gear position.When the six speed gear assembly 10 is in the 5th gear position, 3–4shift ring 24 and the 1–2 shift ring 46 are each in their neutralpositions, while the 5–6 shift ring 34 is engaged with the mainshaft 5thgear 36, which causes the mainshaft 5th gear 36 to be non-rotatablycoupled to the mainshaft 12. Regardless that the countershaft 5th gear50 is non-rotatably coupled to the countershaft 14, torque is nottransferred between the mainshaft 12 and the countershaft 14. Torque istransferred from the mainshaft to the 5–6 shift ring 34 to 5th gear 36as shown by arrow 248. Torque is then transferred from the output gear360 of the mainshaft 5th gear 36 to the drive belt to drive the rearwheel of the motorcycle.

FIG. 20 shows the six speed gear assembly 10 in the 6th gear position.When the six speed gear assembly 10 is in the 6th gear position, 3–4shift ring 24 and the 1–2 shift ring 46 are each in their neutralpositions, while the 5–6 shift ring 34 is engaged with the mainshaft 6thgear 32, which causes the mainshaft 6th gear 32 to be non-rotatablycoupled to the mainshaft 12. Since the countershaft 6th gear 49 isnon-rotatably coupled to the countershaft 14, torque is transferredbetween the mainshaft 12 and the countershaft 14 by the mainshaft 6thgear 32 and the countershaft 6th gear 49; and since the countershaft 5thgear 50 is non-rotatably coupled to the countershaft 14, torque istransferred to the mainshaft 5th gear 36 as shown by arrow 250. Torqueis then transferred from the output gear 360 of the mainshaft 5th gear36 to the drive belt to drive the rear wheel of the motorcycle.

FIGS. 21A–21C show details of the gear shifting assembly 192. FIG. 21Ashows the detent track 228; FIG. 28B shows an arrangement of the shiftpins 224 on the shift drum 192; and FIG. 21C shows a flattened depictionof the cylindrical surface of the shift drum 194, including the shiftdrum grooves 196A–196D.

As shown in FIG. 21A, the detent track 228 has six equally spaced spokes256 a–256 f that define six valleys 252 a–252 f. An indention in thespoke 256 f defines a seventh valley 252 g. When the shift pawl 258rotates the shift drum 194 by manipulation of the shift pins 224 asdescribed below, the roller 227 on the second end 226B of the detentfollower 226 rides along the spokes 256 b–256 f and is biased into oneof the seven valleys 252 a–252 g. As such, the shift drum 194 is biasedinto one of seven predetermined positions corresponding to each of theseven positions of the roller 227 of the detent follower 226.

When the roller 227 is in the valley 252 g, the shift forks 198, 202 and206 are disposed in their corresponding grooves 196A, 196C and 196D,respectively, along the line labeled “Neutral” in FIG. 21C. In thisposition, none of the shift rings 24, 34 and 46 are engaged with acorresponding six speed gear assembly gear, thus the six speed gearassembly 10 is in the neutral gear position as shown in FIG. 14.

When the roller 227 is in the valley 252 a, as shown in FIG. 21A, theshift forks 198, 202 and 206 are disposed in their corresponding groovesare along the line labeled “1st” in FIG. 21C and the 1–2 shift drumgroove 196 c causes the 1–2 shift fork 202 to move the 1–2 shift ring 46into engagement with the countershaft 1st gear 42. In this position, thesix speed gear assembly 10 is in the 1st gear position as shown in FIG.15.

When the roller 227 is in the valley 252 f, the shift forks 198, 202 and206 are disposed in their corresponding grooves along the line labeled“2nd” in FIG. 21C and the 1–2 shift drum groove 196 c causes the 1–2shift fork 202 to move the 1–2 shift ring 46 into engagement with thecountershaft 2nd gear 48. In this position, the six speed gear assembly10 is in the 2nd gear position as shown in FIG. 16.

When the roller 227 is in the valley 252 e, the shift forks 198, 202 and206 are disposed in their corresponding grooves along the line labeled“3rd” in FIG. 21C and the 3–4 shift drum groove 196 a causes the 3–4shift fork 198 to move the 3–4 shift ring 24 into engagement with themainshaft 3rd gear 26. In this position, the six speed gear assembly 10is in the 3rd gear position as shown in FIG. 17.

When the roller 227 is in the valley 252 d, the shift forks 198, 202 and206 are disposed in their corresponding grooves along the line labeled“4th” in FIG. 21C and the 3–4 shift drum groove 196 a causes the 3–4shift fork 198 to move the 3–4 shift ring 24 into engagement with themainshaft 4th gear 20. In this position, the six speed gear assembly 10is in the 4th gear position as shown in FIG. 18.

When the roller 227 is in the valley 252 c, the shift forks 198, 202 and206 are disposed in their corresponding grooves along the line labeled“5th” in FIG. 21C and the 5–6 shift drum groove 196 d causes the 5–6shift fork 206 to move the 5–6 shift ring 34 into engagement with themainshaft 5th gear 36. In this position, the six speed gear assembly 10is in the 5th gear position as shown in FIG. 19.

When the roller 227 is in the valley 252 b, the shift forks 198, 202 and206 are disposed in their corresponding grooves along the line labeled“6th” in FIG. 21C and the 5–6 shift drum groove 196 d causes the 5–6shift fork 206 to move the 5–6 shift ring 34 into engagement with themainshaft 6th gear 32. In this position, the six speed gear assembly 10is in the 6th gear position as shown in FIG. 20.

FIG. 22 shows the shift pawl 258. The shift pawl 258 includes a shiftershaft 262. Attached to the shifter shaft 262 is a main body 264 of theshift pawl 258. The main body 264 extends generally perpendicularly fromthe shifter shaft 262. The main body 264 includes a shift lever 266 andan over-downshift protection arm 268. Attached to the shift lever 266 isa ratchet arm 270. The ratchet arm 270 includes a recess 286 defined byfirst and second fingers 288 and 290. The first finger 288 includes aramped portion 292 and the second finger 290 includes a ramped portion292B.

A main body torsion spring 274 is mounted around an outer surface of theshifter shaft 262 and has first and second arms 276 and 278 in contactwith opposite sides of a spring mounting plate 280. The main bodytorsion spring 274 resists rotation of the shift pawl 258 in eitherdirection.

A ratchet arm torsion spring 282 is mounted around a mounting pin 284,which rotatably connects the shift lever 266 of the main body 264 to theratchet arm 270. The ratchet arm torsion spring 282 includes a first arm294 in contact with the ratchet arm 270 and a second arm 296 in contactwith the shift lever 266 of the main body 264. The ratchet arm torsionspring 282 resists rotation of the ratchet arm 270 in a direction awayfrom the main body 264 (the counter-clockwise direction in FIG. 22.)

As shown in FIG. 9, the shifter shaft 262 of the shift pawl 258 ismounted through opening 260 in the side wall 19 of the modified stocktransmission case 9′ from the cavity 23 area of the transmission case 9′and is rotatably supported by the shifter rod lever 125. For example, inone embodiment, an end of the shifter shaft 262 has external teeth 272that are engaged by the shifter rod lever 125. The shifter rod lever 125rotates in response to a motorcycle operator actuating a shift pedal(not shown), which in turn causes a corresponding rotation of the shiftpawl 258.

As shown in FIGS. 23A–23C, the ratchet arm 270 is biased into contactwith the shift pins 224 (individually labeled in FIGS. 23A–23C as shiftpins 224 a–224 f) such that rotation of the shift pawl 258 causes theratchet arm 270 to corresponding rotate the shift pins and hence theshift drum 194.

FIGS. 23A–23C illustrate a down-shifting operation of the ratchet arm270. FIG. 23A illustrates an exemplary position of the shift pawl 258 ina resting state. In this depiction, adjacent shift pins 224 a and 224 fare disposed in the recess 286 of the ratchet arm 270 and in contactwith the first and second fingers 288 and 290, respectively.

During a downshifting operation, the shifter rod lever 125 rotates theshift pawl 258 in a counter-clockwise direction. The causes the ratchetarm 270 to pull shift pin 224 f to the left as shown in FIG. 23B,causing a counter-clockwise rotation of the shift drum 194. When theshift drum 194 has rotated sufficient for one full gear change, theover-downshift protection arm 268 contacts shift pin 224 b to prevent afurther counter-clockwise rotation of the shift drum 194. Thus, theshift drum 194 cannot be over rotated, allowing for downshifting by onlyone gear.

When the over-downshift protection arm 268 contacts shift pin 224 b, themain body torsion spring 274 rotates the shift pawl 258 in a clockwisedirection and back into the resting position as shown in FIG. 23C. Asthe shift pawl 258 is so rotated, the ramped portion 292 of the secondfinger 290 of the ratchet arm 270 contacts the shift pin 224 e allowingthe second finger 290 to move over and around the shift pin 224 ewithout rotating the shift drum 194. When the second finger 290 movespast the shift pin 224 e, the ratchet arm torsion spring 282 biases theratchet arm 270 over the shift pin 224 e such that the shift pin 224 eis disposed with the recess 286 of the ratchet arm 270 and in contactwith the second finger 290.

Viewing FIGS. 1 and 9 together, the six speed gear assembly 10 may beretrofitted to a stock five speed transmission case 9 by removing thestock trapdoor 21 from the stock five speed transmission case 9;securing the six speed gear assembly 10 to the trapdoor 130; andsecuring the trapdoor 130 to the stock five speed transmission case 9.The end cover 186 may be secured to the trapdoor 130 as described above.The shifting assembly 192 or a conventional shifting assembly 75 may beattached to the top surface 89 of the central portion 13 of thetransmission case 9. If the 3–4 shift fork 198 is used, the shift forkshaft mounting flange 101 must be removed from the stock five speedtransmission case 9, forming the modified stock transmission case 9′ ofFIG. 9, which allows for the appropriate axial movement of the 3–4 shiftfork 198 relative to the six speed gear assembly 10. The ratchet arm 270or the conventional ratchet arm 127 may be attached to the selectedshifting assembly 192 or 75 to cause rotations of the selected shiftdrum 194 or 77.

Alternatively, the six speed gear assembly 10 may be secured to thetrapdoor 130 or to a conventional trapdoor, such as trapdoor 21; andsecured with the selected trapdoor 130 or 21 to a new transmission case(not shown), which may be larger than or substantially the same size asthe stock five speed transmission case 9. The end cover 186 or aconventional end cover (not shown) may be secured to the selectedtrapdoor 130 or 21. The shifting assembly 192 or a conventional shiftingassembly 75 may be attached to a top surface of a central portion of thenew transmission case. The ratchet arm 270 or the conventional ratchetarm 127 may be attached to the selected shifting assembly 192 or 75 tocause rotations of the selected shift drum 194 or 77.

The preceding description has been presented with references topresently preferred embodiments of the invention. Persons skilled in theart and technology to which this invention pertains will appreciate thatalterations and changes in the described structures and methods ofoperation can be practiced without meaningfully departing from theprinciple, spirit and scope of this invention. Accordingly, theforegoing description should not be read as pertaining only to theprecise structures described and shown in the accompanying drawings.

1. A six speed gear assembly for a motorcycle transmission comprising: amainshaft gear shaft; a plurality of mainshaft gears mounted in sequenceon the mainshaft and comprising: a mainshaft 4th gear, a mainshaft 3rdgear, a gear chosen from the group consisting of a mainshaft 1st gearand a mainshaft 2nd gear, a remaining gear from the group consisting ofthe mainshaft 1st gear and the mainshaft 2nd gear, a mainshaft 6th gear,and a mainshaft 5th gear, wherein respective gear diameter of themainshaft gears successively increases from mainshaft 1st gear tomainshaft 2nd gear to mainshaft 3rd gear to mainshaft 4th gear tomainshaft 5th gear to mainshaft 6th gear; a countershaft gear shaft; anda plurality of countershaft gears mounted in sequence on thecountershaft and comprising: a countershaft 4th gear, a countershaft 3rdgear, a gear chosen from the group consisting of a countershaft 1st gearand a countershaft 2nd gear, a remaining gear from the group consistingof the countershaft 1st gear and the countershaft 2nd gear, acountershaft 6th gear, and a countershaft 5th gear, wherein respectivegear diameter of the countershaft gears successively increases fromcountershaft 6th gear to countershaft 5th gear to countershaft 4th gearto countershafi 3rd gear to countershaft 2nd gear to countershaft 1stgear.
 2. The six speed gear assembly of claim 1, wherein each mainshaftgear is axially restrained relative to the mainshaft and wherein eachcountershaft gear is axially restrained relative to the countershaft. 3.The six speed gear assembly of claim 2, wherein each mainshaft gearmeshes in 100% gear mesh engagement with a corresponding countershaftgear.
 4. The six speed gear assembly of claim 1, wherein each mainshaftgear meshes with a corresponding countershaft gear to form a pluralityof gear couplings, and wherein one of the gears from each gear couplingis rotatably coupled to its corresponding gear shaft and the remaininggear from each gear coupling is non-rotatably coupled to itscorresponding gear shaft.
 5. The six speed gear assembly of claim 4,wherein each rotatably coupled gear is removably engaged by acorresponding one of a plurality of shift rings, and wherein each shiftring is non-rotatably coupled to a corresponding one of the gear shafts.6. The six speed gear assembly of claim 4, wherein each rotatablycoupled gear comprises pockets that are removably engaged by dogs thatprotrude from a corresponding one of a plurality of shift rings, andwherein each shift ring is non-rotatably coupled to a corresponding oneof the gear shafts.
 7. The six speed gear assembly of claim 5, whereineach shift ring is disposed between a corresponding pair of therotatably coupled gears.
 8. The six speed gear assembly of claim 7,wherein each shift ring is axially movable relative to its correspondinggear shaft to selectively engage a desired one of the gears in itscorresponding rotatably coupled gear pair.
 9. The six speed gearassembly of claim 7, wherein each shift ring is axially movable relativeto its corresponding gear shaft and comprises a body having a firstplurality of dogs protruding from a first side of its body toselectively engage the pockets of one of the gears in its correspondingrotatably coupled gear pair and a second plurality of dogs protrudingfrom a second side of its body to selectively engage the pockets of theremaining gear in its corresponding rotatably coupled gear pair.
 10. Asix speed gear assembly for a motorcycle transmission comprising: amainshaft gear shaft; a plurality of mainshaft gears mounted on themainshaft and comprising 1st, 2nd, 3rd, 4th, 5th and mainshaft 6thgears; a countershaft gear shaft; a plurality of countershaft gearsmounted on the countershaft and comprising 1st, 2nd, 3rd, 4th, 5th andcountershaft 6th gears; and wherein each mainshaft gear meshes with acorresponding countershaft gear to form a plurality of gear couplings,the gear couplings having respective gear ratios which successivelyincrease from the 1st gear coupling to the 2nd gear coupling to the 3rdgear coupling to the 4th gear coupling to the 5th gear coupling to the6th gear coupling; wherein one of the gears from each gear coupling isrotatably coupled to its corresponding gear shaft and the remaining gearfrom each gear coupling is non-rotatably coupled to its correspondinggear shaft; and wherein each rotatably coupled gear is removably engagedby one of a plurality of shift rings, each shift ring forming anindependent component of the motorcycle transmission.
 11. The six speedgear assembly of claim 10, wherein each shift ring is non-rotatablycoupled to a corresponding one of the gear shafts.
 12. The six speedgear assembly of claim 11, wherein each rotatably coupled gear comprisespockets that are removably engaged by dogs that protrude from one of theplurality of shift rings.
 13. The six speed gear assembly of claim 11,wherein each shift ring is disposed between a corresponding pair of therotatably coupled gears.
 14. The six speed gear assembly of claim 13,wherein each shift ring is axially movable relative to its correspondinggear shaft to selectively engage a desired one of the gears in itscorresponding rotatably coupled gear pair.
 15. The six speed gearassembly of claim 13, wherein each shift ring is axially movablerelative to its corresponding gear shaft and comprises a body having afirst plurality of dogs protruding from a first side of its body toselectively engage the pockets of one of the gears in its correspondingrotatably coupled gear pair and a second plurality of dogs protrudingfrom a second side of its body to selectively engage the pockets of theremaining gear in its corresponding rotatably coupled gear pair.
 16. Thesix speed gear assembly of claim 11, wherein each mainshaft gear isaxially restrained relative to the mainshaft and wherein eachcountershaft gear is axially restrained relative to the countershaft.17. The six speed gear assembly of claim 16, wherein each mainshaft gearmeshes in 100% gear mesh engagement with a corresponding countershaftgear.
 18. A method of retrofitting a six speed motorcycle transmissionto a five speed transmission case, wherein the case comprises a centralportion, a first side wall adjacent to a first side of the centralportion, and a trapdoor adjacent to a second side of the centralportion, wherein the central portion comprises a top surface and acentral portion opening, the method comprising: removing the trapdoor;providing a six speed gear assembly comprising a mainshaft gear shaftand a countershaft gear shaft; mounting a plurality of mainshaft gearson the mainshaft, wherein the plurality of mainshaft gears comprisesmainshaft 1st, 2nd, 3rd, 4th, 5th and 6th gears; mounting a plurality ofcountershaft gears on the countershaft, wherein the plurality ofcountershaft gears comprises countershaft 1st, 2nd, 3rd, 4th, 5th and6th gears, wherein each mainshaft gear meshes with a correspondingcountershaft gear to form a plurality of gear couplings; securing thesix speed gear assembly to a replacement trapdoor, the replacementtrapdoor comprising a recess that receives at least a portion of thethickness of one of the gear couplings; and securing the replacementtrapdoor and the six speed gear assembly to the stock case.
 19. Themethod of claim 18, wherein the six speed gear assembly is secured tothe replacement trapdoor, such that the recess of the replacementtrapdoor receives at least a majority of the thickness of one of thegear couplings.
 20. The method of claim 18, wherein the mainshaft 4thgear meshes with the countershaft 4th gear to form one of the pluralityof gear couplings and wherein the six speed gear assembly is secured tothe replacement trapdoor, such that the recess of the replacementtrapdoor receives at least a portion of the thickness of each of themainshaft 4th gear and the countershaft 4th gear.
 21. The method ofclaim 20, further comprising mounting a speedo sensor to the trapdoor inclose proximity to the mainshaft 4th gear.
 22. The method of claim 18,wherein the mainshaft 4th gear meshes with the countershaft 4th gear toform one of the plurality of gear couplings and wherein the six speedgear assembly is secured to the replacement trapdoor, such that therecess of the replacement trapdoor receives at least a majority of thethickness of each of the mainshaft 4th gear and the countershaft 4thgear.
 23. The method of claim 18, wherein mounting the plurality ofmainshaft gears on the mainshaft gear shaft comprises mounting eachmainshaft gear such that each mainshaft gear is axially restrainedrelative to the mainshaft gear shaft and wherein mounting the pluralityof countershaft gears on the countershaft gear shaft comprises mountingeach countershaft gear such that each countershaft gear is axiallyrestrained relative to the countershaft gear shaft.
 24. The method ofclaim 18, wherein each of the plurality of gear couplings meshes in 100%gear mesh engagement.
 25. The method of claim 18, wherein one of thegears from each gear coupling is rotatably coupled to its correspondinggear shaft and the remaining gear from each gear coupling isnon-rotatably coupled to its corresponding gear shaft.
 26. The method ofclaim 25, wherein each rotatably coupled gear is removably engaged by acorresponding one of a plurality of shift rings, and wherein each shiftring is non-rotatably coupled to a corresponding one of the gear shafts.27. The method of claim 25, wherein each rotatably coupled gearcomprises pockets that are removably engaged by dogs that protrude froma corresponding one of a plurality of shift rings, and wherein eachshift ring is non-rotatably coupled to a corresponding one of the gearshafts.
 28. The method of claim 26, wherein each shift ring is disposedbetween a corresponding pair of the rotatably coupled gears.
 29. Themethod of claim 28, wherein each shift ring is axially movable relativeto its corresponding gear shaft to selectively engage a desired one ofthe gears in its corresponding rotatably coupled gear pair.
 30. Themethod of claim 28, wherein each shift ring is axially movable relativeto its corresponding gear shaft and comprises a body having a firstplurality of dogs protruding from a first side of its body toselectively engage the pockets of one of the gears in its correspondingrotatably coupled gear pair and a second plurality of dogs protrudingfrom a second side of its body to selectively engage the pockets of theremaining gear in its corresponding rotatably coupled gear pair.
 31. Themethod of claim 18, further comprising: mounting a 3–4 shift ring on acorresponding one of the gear shafts and disposing the 3–4 shift ringbetween one of the gear couplings chosen from the group consisting ofthe 4th and mainshaft 3rd gears and the 4th and countershaft 3rd gears,such that that the 3–4 shift ring selectively engages a desired one ofthe gear couplings chosen from the group consisting of the 4th andmainshaft 3rd gears and the 4th and countershaft 3rd gears; andproviding a 3–4 shift fork comprising a fork arm that engages a groovein the 3–4shift ring to axially move the 3–4 shift ring relative to itscorresponding gear shaft, wherein the 3–4 shift fork comprises an armconnected to the fork arm and extending across at least two gears of acorresponding gear shaft.
 32. The method of claim 18, furthercomprising: mounting a shift ring on a corresponding one of the gearshafts and disposing the shift ring between two of the gear couplingssuch that the shift ring is selectively engagable to a desired one ofthe two gear couplings; and mounting a shift fork on the shift ring suchthat a fork arm engages a groove in the shift ring to axially move theshift ring relative to its corresponding gear shaft, wherein the shiftfork comprises an arm connected to the fork arm that extends across atleast two gears of a corresponding gear shaft.
 33. The method of claim18, further comprising: mounting a shifting assembly to the top surfaceof the central portion of the transmission case; mounting a shift ringto the shifting assembly, wherein the shift ring comprising a fork arm,and an elongated arm extending generally perpendicularly from the forkarm, wherein when the fork arm is disposed in close proximity to thereplacement trapdoor, the elongated arm extends over at least two gearsof a corresponding gear shaft, while a pin extends from the fork arm,through the central portion opening and into engagement with a recessedgroove in a shift drum of the shifting assembly.
 34. The method of claim18, further comprising: providing a replacement end cover having arecess; forming a protrusion that extends from a portion of thereplacement trapdoor; inserting the protrusion of the replacementtrapdoor into the recess of the cover such that a rotation movement ofthe replacement end cover relative to the replacement trapdoor isprevented.
 35. The method of claim 18, further comprising: mounting theplurality of mainshaft gears on the mainshaft gear shaft in a sequencethat comprises: the mainshaft 4th gear, the mainshaft 3rd gear, a gearchosen from the group consisting of the mainshaft 1st gear and themainshaft 2nd gear, a remaining gear from the group consisting of themainshaft 1st gear and the mainshaft 2nd gear, the mainshaft 6th gear,and the mainshaft 5th gear; and mounting the plurality of countershaftgears on the countershaft gear shaft in a sequence that comprises: thecountershaft 4th gear; the countershaft 3rd gear; a gear chosen from thegroup consisting of the countershaft 1st gear and the countershaft 2ndgear; a remaining gear from the group consisting of the countershaft 1stgear and the countershaft 2nd gear; the countershaft 6th gear; and thecountershaft 5th gear.
 36. The method of claim 18, wherein the casefurther comprises a shift fork shaft mounting flange for mountinglyreceiving a shift fork shaft of a shifting assembly, the method furthercomprising removing the shift fork shaft mounting flange.
 37. The methodof claim 36, further comprising: forming a shift fork shaft opening inthe replacement trapdoor; providing a shift fork shaft; and mounting anend of a shift fork shaft in the shift fork shaft opening of thereplacement trapdoor.
 38. The method of claim 18, wherein the casefurther comprises a shift pawl, the method further comprising: removingthe shift pawl; mounting a replacement shift pawl to a shifting assemblythat comprises a shift drum having a plurality of shift pins, such thatmovements of the shift pins causes up shifting and downshifting of thegears, wherein the shift pawl comprises a ratchet arm connected to atleast one of the shift pins for causing the up-shifting and adown-shifting of the gears, and wherein the shift pawl further comprisesa second arm that prevents the ratchet arm from down shifting by morethan one gear.
 39. The method of claim 38, wherein the second arm is anover-downshift protection arm.
 40. The method of claim 18, wherein thesix speed motorcycle transmission is retrofitted to the five speedtransmission case without modifying an overall length of the five speedtransmission case.
 41. A trapdoor for retrofitting to a five speedtransmission case, the trapdoor comprising: a trapdoor base; and arecess in the trapdoor base for receiving at least a portion of thethickness of a gear from a six speed gear assembly, the six speed gearassembly comprising: a mainshaft 1st gear, a mainshaft 2nd gear, amainshaft 3rd gear, a mainshaft 4th gear, a mainshaft 5th gear, and amainshaft 6th gear, wherein respective gear diameter of the mainshaftgears successively increases from mainshaft 1st gear to mainshaft 2ndgear to mainshaft 3rd gear to mainshaft 4th gear to mainshaft 5th gearto mainshaft 6th gear; and a countershaft 1st gear, a countershaft 2ndgear, a countershaft 3rd gear, a countershaft 4th gear, a countershaft5th gear, and a countershaft 6th gear, wherein respective gear diameterof the mainshaft gears successively increases from countershaft 6th gearto countershaft 5th gear to countershaft 4th gear to countershaft 3rdgear to countershaft 2nd gear to countershaft 1st gear.
 42. The trapdoorof claim 41, wherein said gear from the six speed gear assembly that isreceived by the recess of the trapdoor is the mainshaft 4th gear. 43.The trapdoor of claim 41, wherein the recess of the trapdoor comprises alength sufficient for receiving the length of a meshed gear couplingfrom the six speed gear assembly.
 44. The trapdoor of claim 43, whereinsaid meshed gear coupling from the six speed gear assembly that isreceived by the length of the recess of the trapdoor is a meshed gearcoupling of the mainshaft 4th gear and the countershaft 4th gear. 45.The trapdoor of claim 41, further comprising a protrusion extending fromthe trapdoor base for engagement with a recess in an end cover, suchthat when the protrusion of the trapdoor is inserted into the recess ofthe end cover, a rotational movement of the trapdoor relative to the endcover is prevented.
 46. A trapdoor for a motorcycle transmissioncomprising: a trapdoor base; and a recess in the trapdoor base forreceiving at least a portion of the thickness of a gear from atransmission gear assembly, the transmission gear assembly comprising: amainshaft 1st gear, a mainshaft 2nd gear, a mainshaft 3rd gear, amainshaft 4th gear, a mainshaft 5th gear, and a mainshaft 6th gear,wherein respective gear diameter of the mainshaft gears successivelyincreases from mainshaft 1st gear to mainshaft 2nd gear to mainshaft 3rdgear to mainshaft 4th gear to mainshaft 5th gear to mainshaft 6th gear;and a countershaft 1st gear, a countershaft 2nd gear, a countershaft 3rdgear, a countershaft 4th gear, a countershaft 5th gear, and acountershaft 6th gear, wherein respective gear diameter of the mainshaftgears successively increases from countershaft 6th gear to countershaft5th gear to countershaft 4th gear to countershaft 3rd gear tocountershaft 2nd gear to countershaft 1st gear.
 47. The trapdoor ofclaim 46, wherein said gear from the transmission gear assembly that isreceived by the recess of the trapdoor is the mainshaft 4th gear. 48.The trapdoor of claim 46, wherein the recess of the trapdoor comprises alength sufficient for receiving the length of a meshed gear couplingfrom the transmission gear assembly.
 49. The trapdoor of claim 48,wherein said meshed gear coupling from the transmission gear assemblythat is received by the length of the recess of the trapdoor is a meshedcoupling of the mainshaft 4th gear and the countershaft 4th gear. 50.The trapdoor of claim 46, further comprising a protrusion extending fromthe trapdoor base for engagement with a recess in an end cover, suchthat when the protrusion of the trapdoor is inserted into the recess ofthe end cover, a rotational movement of the trapdoor relative to the endcover is prevented.
 51. A trapdoor and end cover combination for amotorcycle transmission comprising: a trapdoor base having a protrusionextending therefrom; and an end cover base having a recess formedtherein, wherein the protrusion of the trapdoor mates with the recess inthe end cover to prevent a rotational movement of the trapdoor relativeto the end cover.
 52. A transmission assembly comprising: a six speedgear assembly comprising a mainshaft gear shaft and a countershaft gearshaft; a plurality of mainshaft gears mounted on the mainshaft, whereinthe plurality of mainshaft gears comprises mainshaft 1st, 2nd, 3rd, 4th,5th and 6th gears, and wherein respective gear diameter of the mainshaftgears successively increases from mainshaft 1st gear to mainshaft 2ndgear to mainshaft 3rd gear to mainshaft 4th gear to mainshaft 5th gearto mainshaft 6th gear; a plurality of countershaft gears mounted on thecountershaft, wherein the plurality of countershaft gears comprisescountershaft 1st, 2nd, 3rd, 4th, 5th and 6th gears, wherein respectivegear diameter of the countershaft gears successively increases fromcountershaft 6th gear to countershaft 5th gear to countershaft 4th gearto countershaft 3rd gear to countershaft 2nd gear to countershaft 1stgear, and wherein a mainshaft gear meshes with a correspondingcountershaft gear to form a gear coupling; and a trapdoor comprising arecess that receives at least a portion of the thickness of one of thegears.
 53. The transmission assembly of claim 52, wherein the recessreceives at least a majority of the thickness of one of the gears. 54.The transmission assembly of claim 52, wherein the mainshaft 4th gearmeshes with the countershaft 4th gear to form said gear coupling andwherein the recess of the trapdoor receives at least a portion of thethickness of the mainshaft 4th gear.
 55. The transmission assembly ofclaim 54, further comprising a speedo sensor mounted within the recessof the trapdoor and in close proximity to the mainshaft 4th gear. 56.The transmission assembly of claim 52, wherein the mainshaft 4th gearmeshes with the countershaft 4th gear to form said gear coupling andwherein the recess of the trapdoor receives at least a majority of thethickness of the mainshaft 4th gear.